问题如下：
LIFO reserve is most likely to increase when inventory unit:
选项：
A. costs are increasing.
B. costs are decreasing.
C. levels are decreasing.
解释：
A is correct.
LIFO reserve is the FIFO inventory value less the LIFO inventory value. In periods of rising inventory unit costs, the carrying amount of inventory under FIFO will always exceed the carrying amount of inventory under LIFO. The LIFO reserve may increase over time as a result of the increasing difference between the older costs used to value inventory under LIFO and the more recent costs used to value inventory under FIFO. When inventory unit levels are decreasing, the company will experience a LIFO liquidation, reducing the LIFO reserve.
老师，请问为什么 inventory unit level decrease时一定会有lifo liquidation？lifo liquidation不是一种主动选择吗，主动选择不进新货卖便宜存货？
